1. Field of the Invention
This invention relates to a novel synthesis for the preparation of benzoxazine compounds from phenolic compounds, aldehyde compounds, and amine compounds.
2. Brief Description of Related Technology
Benzoxazines are ordinarily prepared by reacting a phenolic compound, with an aldehyde and an alkyl amine. This reaction is known to be conducted under solventless conditions or in a solvent, such as toluene, dioxane, alcohol or diethyl ether.
For instance, in U.S. Pat. No. 5,543,516 (Ishida) a method for preparing a benzoxazine compound is provided, in which a reaction mixture containing a phenolic compound, a primary amine, and an aldehyde is prepared without a separate solvent; the reactants are brought to a temperature at which the reactants combine chemically and are maintained at that temperature to reportedly form the benzoxazine compound.
And Chinese Patent Publication No. CN 1451679 (Cu) is directed to modified benzoxazine resins for RTM applications, and explains that in the past benzoxazine resins had been synthesized using organic solvents, such as toluene, dioxane and dimethyl benzene (citing to Chinese Patent Application No. ZL 94111852.5). In the CN '679 publication, however, toluene is used as the solvent in the working examples.
Benzoxazines are presently available from several sources commercially, including Huntsman Specialty Chemicals, Brewster, N.Y.; Georgia-Pacific Resins, Inc. and Shikoku Chemicals Corporation, Chiba, Japan, the last of which offers among others B-a, B-m, F-a, C-a and F-a benzoxazine resins. It is believed that these commercially available benzoxazines are prepared using toluene as a solvent.
However, these known synthetic methods and some commercial benzoxazines have shortcomings. For instance, some of the solvents used in the synthesis are toxic and thus desirably are avoided in the workplace, while others are removable at elevated temperature conditions that cause a premature degradation and/or polymerization of some benzoxazine compounds, resulting in compromised performance of curable compositions formulated with such benzoxazines.
The known synthetic method usually takes a relatively long period of time, i.e., at least several hours, to carry out the desired reaction, and to separate the reaction products. Purification of the end product oftentimes requires additional time. In addition, although the yield of benzoxazines is in many cases satisfactory, as noted many common solvents pose toxicity risks, which in many cases require expensive measures to eliminate, for instance the installation of costly solvent recovery systems.
There therefore exists a need for a synthetic method that overcomes these shortcomings.